Apparatus and method for facilitating terrestrial transmissions at frequencies also used for satellite transmissions to a common geographic area

ABSTRACT

A satellite receiving antenna ( 16 ) at a user location ( 14 ) receives satellite signals at a first frequency from a satellite ( 12 ). The satellite signals travel along a satellite signal route ( 42 ) within a look angle about the centerline ( 28 ) of the antenna ( 16 ). A terrestrial transmitter ( 20 ) transmits signals at the first frequency along a wireless transmission route ( 40 ) from the transmitter to the user location ( 14 ). The terrestrial transmitter ( 20 ) is located with respect to the user location ( 14 ) so that the wireless transmission route ( 40 ) is at a relatively large angle to the centerline ( 28 ) of the first antenna ( 16 ). The angle of the wireless transmission route ( 40 ) to the satellite antenna centerline ( 28 ) is large enough so that the terrestrial signals present at the location ( 14 ) result in terrestrial input signals from the antenna ( 16 ) which are less than an interference level with respect to satellite input signals produced by the antenna. Thus, the terrestrial signals do not interfere with the satellite signals even though they are transmitted at a common frequency.

This application is a continuation-in-part of application Ser. No.08/731,244 filed Oct. 11, 1996, now U.S. Pat. No. 5,761,605.

BACKGROUND OF THE INVENTION

This invention relates to apparatus and methods for broadcasting andreceiving data, including digital television signals, voice signals, andother data. More particularly, this invention relates to an apparatusand method for providing terrestrial transmissions simultaneously alongwith direct broadcast satellite transmissions on a common frequency andfor setting the transmission power level for the terrestrialtransmissions.

Currently, television signals may be received from a satellite ingeosynchronous orbit about the earth. The television signals aretransmitted from a terrestrial transmitter to the satellite, perhapscommunicated between different satellites, and then retransmitted from asatellite so that the signals can be received by terrestrial receiverswithin a certain geographic receiving area within a line of sight of thesatellite. In addition to television signals, other types of data mayalso be transmitted to consumers through satellites in eithergeosynchronous or non-geosynchronous orbit.

Direct broadcast satellite service (DBS) refers to satellitetransmission of television signals and other data directly for use byindividual households or subscribers having the proper signal receivingequipment. The U.S. Federal Communications Commission has dedicated theelectromagnetic spectrum from 12.2 gigahertz to 12.7 gigahertz for DBSbroadcasting. Numerous signal carriers are located within the DBSspectrum, each carrier carrying several individual television channels.Depending upon the compression technology applied to these signals,literally hundreds of separate channels may be available through DBS. Agreat benefit of the DBS system as opposed to prior satellite systems isthat only a small dish-type antenna is required to receive the DBSsignals and the alignment of the receiving dish is not as critical asearlier satellite broadcast systems. Also, the DBS system will providehigh quality reception at any point in the geographic receiving area ofa satellite without the expense of land transmission lines such as thoserequired for cable television.

Current regulations require that DBS satellites be separated from eachother by at least nine (9) degrees in a geosynchronous arc. Thereceiving antenna for DBS signals must, therefore, be limited toreceiving signals in a directional range measuring plus or minus nine(9) degrees from a centerline of the antenna. Receiving signals in arange wider than the satellite spacing would cause interference bysignals transmitted by different satellites on the same frequency. Thelimited directional reception range of the DBS receiving antenna is theresult of the gain provided by the antenna being asymmetrical about theantenna structure. DBS signals reaching the DBS receiving antenna atangles outside of the directional range of the antenna receiveinsufficient gain to interfere with the desired DBS signals receivedwithin the antenna directional range.

U.S. Pat. No. 5,483,663 is directed to a system having a receiverarrangement in which DBS and terrestrial signals are received withinsimilar frequency bands. The system shown in the 5,483,663 Patent may beimplemented with a multiple antenna arrangement, or with a single,moveable antenna. In the multiple antenna arrangement, two separateantennas direct the received signals to a common propagation path forprocessing as if they were received by a single antenna and transmittedfrom a single location. In the single antenna arrangement, the antennais movable between a position to receive DBS signals and anotherposition to receive terrestrial signals.

The advantage of the system shown in U.S. Pat. No. 5,483,663 is thatlocal originating signals, whether carrying data for television or otherdata, may be received simultaneously with DBS signals, and processedwith the same or similar equipment as that used to process the DBSsignals. The local originating signals may carry local televisionprogramming which may be received along with the national or regionalDBS television programming.

SUMMARY OF THE INVENTION

It is an object of the invention to provide terrestrially transmittedsignals simultaneously with satellite transmitted signals at the samefrequency. The invention includes an apparatus and method for use intransmitting terrestrial signals simultaneously with satellite signalstransmitted at a common frequency.

The object of the invention is accomplished by transmitting terrestrialsignals in a manner which ensures that they do not interfere withsatellite signals transmitted at the same frequency. Embodiments of theinvention may take advantage of receiving antennae having a limiteddirectional reception range or look angle and may include transmittingthe terrestrial signals in a different range of directions than those inwhich the satellite signals are transmitted. The power level at whichthe terrestrial signals are transmitted and the directional nature ofthe satellite receiving antennae ensure that the satellite transmittedsignals can be discriminated from the terrestrially transmitted signals.Although the terrestrial signal transmission power is limited to anon-interfering transmission power level, the terrestrial transmissionis still strong enough to produce a usable signal at a distant location.

Several different signals will be discussed in this disclosure. The term“satellite signals” refers to signals transmitted directly from asatellite, whereas the term “terrestrial signals” refers to signalstransmitted directly from a terrestrial transmitter. “Satellite inputsignals” refers to signals resulting from satellite signals which havebeen picked up by an antenna and subjected to gain provided by theantenna. Finally, “terrestrial input signals” refers to signalsresulting from terrestrial signals which have been picked up by anantenna and subjected to gain provided by the antenna.

The invention is employed in the situation in which satellite signalsare transmitted at a satellite transmission frequency to a terrestriallocation. The satellite signals travel along a satellite signal routefrom the satellite to the terrestrial location and to a satellitereceiving antenna at the location for receiving the satellite signals.In some embodiments of the invention, the satellite receiving antenna isomni-directional, that is, provides generally the same gain regardlessof the direction from which the signals reach the antenna. In otherforms of the invention, the satellite receiving antenna has adirectional reception characteristic in which the gain provided by theantenna reaches a peak along an antenna centerline and generallydecreases as the angle from the centerline increases.

The omni-directional satellite receiving antenna need not be oriented ina particular direction to receive signals from a satellite. However, inorder to receive satellite signals with the directional satellitereceiving antenna, the antenna must be aligned in a satellite receptionposition. In this satellite reception position, the satellite signalroute lies close enough to the antenna centerline that the signalsreceive sufficient gain from the antenna structure to produce satelliteinput signals which are at least at a usable input signal level. Thisminimum usable input signal level represents the minimum input signallevel at which the receiving or signal processing equipment can extractthe desired data.

According to the invention, the terrestrial signals are transmitted atthe same frequency as the satellite signals. The terrestrial signals aretransmitted along a wireless route from the terrestrial transmitter to auser location which may have a satellite receiving antenna. Theinvention avoids interference between the terrestrial and satellitesignals by ensuring that the power level of the terrestrial inputsignals at the satellite receiving antenna is below an interferencelevel with respect to the satellite input signals at the satellitereceiving antenna. The interference level is an input signal power levelwhich is so close in power to the satellite input signal power levelthat the satellite input signals cannot be discriminated ordistinguished. Terrestrial input signals below the interference level donot prevent the receiving or signal processing equipment associated withthe satellite receiving antenna from distinguishing and extracting datafrom the satellite input signals. Also according to the invention,although the terrestrial signals are transmitted so that they do notinterfere with the satellite signals, the terrestrial signals present atthe user location must be strong enough so that they may be received byan appropriately aligned terrestrial receiving antenna at the locationand distinguished from satellite input signals at the terrestrialreceiving antenna. That is, the terrestrial signals present at thelocation must be at least at a minimum usable terrestrial signal level.

Where the satellite receiving antenna is omni-directional, both thesatellite signals and the terrestrial signals picked up by the antennareceive substantially the same gain. Thus for omni-directional satellitereceiving antennae, the terrestrial transmission power level must becontrolled so that the terrestrial signals present at the user locationhave a sufficiently lower power level than the satellite signals presentat the user location.

Where the satellite receiving antenna at the user location is adirectional antenna, the invention may take advantage of the directionalcharacteristic of the antenna and may transmit terrestrial signals at ahigh enough power level while still producing a terrestrial input signalat the satellite receiving antenna which is below the interferencelevel. In the case of the directional satellite receiving antenna, theantenna is oriented in the satellite reception position at the userlocation. The terrestrial transmitter is located with respect to theuser location such that the wireless transmission route from theterrestrial transmitter to the user location is at a relatively largeangle from the satellite receiving antenna centerline. At thisrelatively large angle, the terrestrial signals receive much less gainthan the satellite signals. Thus, the terrestrial signal power level atthe user location may be the same as or even higher than the satellitesignal level and, due to the different gain applied to the signals bythe antenna structure, still result in a terrestrial input signal havinga power level below the interference level with respect to the satelliteinput signal level.

In some applications of the invention, depending upon the direction atwhich a directional satellite receiving antenna must be directed toreceive satellite signals, the terrestrial transmissions may be limitedto a certain azimuth range. This terrestrial transmission azimuth rangeis limited so that it does not include any directions that are withinthe satellite reception look angle of a directional satellite receivingantenna aligned to receive signals from a particular satellite. In orderto cover a large geographic service area for terrestrial signalreception while maintaining the terrestrial transmission power at anon-interfering level, a plurality of terrestrial transmitters may bespaced apart over the area. In this case the effective transmissionareas of the different transmitters combine to ensure the terrestrialsignals may be received clearly at each location within the desiredgeographic service area.

The satellite transmissions and terrestrial transmissions may contain orcarry any type of data including television, internet communications,voice, video, or any other type of data. Although the invention is notlimited to any particular transmission frequencies, the invention isparticularly well adapted for transmission frequencies above onethousand (1000) megahertz. Also, although the invention is not limitedfor use with a particular transmission modulation technique, modulationtechniques such as phase modulation and spectrum spreading (frequencyhopping) are currently preferred.

These and other objects, advantages, and features of the invention willbe apparent from the following description of the preferred embodiments,considered along with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation showing the positions of aplurality of satellites in relation to a single terrestrial transmitterand a receiver or user location.

FIG. 2 is a somewhat schematic representation of a receiving antennastructure for receiving satellite and terrestrial transmitted signals ata common frequency.

FIG. 3 is a schematic representation of the spacing for a number ofterrestrial transmitters required to allow reception over a largegeographic area.

FIG. 4 is a schematic representation of a terrestrial transmitter andterrestrial transmission power control arrangement embodying theprinciples of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An apparatus according to the invention for providing terrestriallytransmitted signals simultaneously on the same frequency used totransmit satellite signals is illustrated in FIG. 1. As shown in FIG. 1,there may be one or more satellites in orbit about the earth. FIG. 1shows four satellites 12 a, 12 b, 12 c, and 12 d spaced apart at fourseparate directions from a user location 14. Satellite receiving antenna16 and terrestrial receiving antenna 18, which will be discussed indetail with reference to FIG. 2, may be located at the user location 14.

Each of these satellites 12 a-d is positioned in geosynchronous orbitabout the center of the earth, and is positioned at a certain longitudeand latitude above the earth's surface. In geosynchronous orbit, eachsatellite remains at a fixed location with respect to the earth'ssurface, and thus, with respect to the user location 14. As is known bythose skilled in the art, a directional receiving antenna may bedirected at a certain elevation and direction or azimuth toward adesired satellite location for receiving signals from the particularsatellite. Of course the satellite signals may be transmitted fromsatellites which are not in geosynchronous orbit. In thisnon-geosynchronous orbit case, the directional satellite receivingantenna can receive satellite signals only as the particular satellitepasses through the directional reception range or look angle of thesatellite receiving antenna, or the antenna must be moved to track thesatellite.

Currently, all direct broadcast satellites within the line of sight ofNorth America are positioned at longitudes and latitudes requiring adirectional receiving antenna to face in a southerly direction fromNorth America to receive signals. Although FIG. 1 shows four satellites12 a-d for purposes of describing the invention, more or fewersatellites may be spaced apart within a line of sight of a certaingeographical area. Regardless of the number of satellites, thedirectional satellite receiving antenna must be directed at a particularazimuth and elevation to receive signals from a particular satellite.The term “azimuth” refers to the direction with respect to a referencedirection such as due north, commonly zero degrees. “Elevation” refersto the angle of the antenna centerline above horizontal. In contrast todirectional receiving antennae, omni-directional antennae need not beoriented in any particular direction in order to receive signals. Thusan omni-directional antenna at the user location 14 would receivesignals equally well from each of the satellites 12 a-d.

DBS satellites all transmit different signals in the same frequencyband. The U.S. Federal Communications Commission has set aside theelectromagnetic spectrum from 12.2 gigahertz to 12.7 gigahertz for DBSbroadcasting. In order to ensure no interference from signals betweentwo adjacent satellites transmitting at the same frequency, twoconditions must be met. First, the satellite receiving antenna must be adirectional antenna and limited to receive signals at the DBS signalstrength only within a certain reception range about the centerline ofthe antenna. Secondly, the satellites must be spaced apart so that areceiving antenna may be positioned with only a single satellitetransmitting in the directional reception range or look angle of theantenna.

According to current regulations, individual DBS satellites must beseparated at least nine (9) degrees in the geosynchronous arc. Thus,each DBS receiving antenna must have a directional reception range, lookangle, or aperture of plus or minus nine (9) degrees or less as measuredfrom a centerline of the antenna. Although current regulations require aspacing of no less than nine (9) degrees separation, the invention isnot limited to use in situations in which the satellites have thisdegree of separation or in which the satellites operate in the currentDBS frequencies.

FIG. 1 also shows a terrestrial transmitter 20 capable of transmittingin one or more frequencies identical to a frequency transmitted by oneof the DBS satellites. The terrestrial transmitter 20 transmitsdirectionally within a certain transmission range or azimuth range T.The transmission range T shown in FIG. 1 is 180 degrees, although therange may be more or less than this number. In some situations, thetransmission range may not be limited but may encompass the entire 360degrees around the transmitter location.

A combined receiving antenna structure 22 which may be at the userlocation 14 in FIG. 1 is illustrated in FIG. 2. The satellite receivingantenna 16 is designed to receive direct broadcast satellite signals andpreferably includes a collecting dish 24 and a feed-horn assembly 26 forreceiving the signals reflected and concentrated by the dish. Thoseskilled in the art will readily appreciate that the feed-horn assembly26 includes a probe and low noise block converter, which are not shownin FIG. 2, for picking up signals directed to the antenna. The receivedsignals, which are defmed herein as “input signals,” are directed fromthe antenna to receiving or signal processing equipment, also not shown,for extracting information or data. This signal processing equipment iswell known in the art and does not form a part of this invention. Also,those skilled in the art will appreciate that numerous types ofassemblies may be used alternatively to the feed-horn assembly 26 forcollecting signals reflected by the dish 24. Furthermore, many othertypes of antennae may be used for receiving the satellite signals.

The satellite receiving antenna 16 is a directional antenna and thus hasthe characteristic that the signal gain produced by the antenna ishighly dependent upon the direction at which the signals reach theantenna. The antenna 16 produces a maximum gain for signals travellingto the structure along an antenna centerline 28. For signals travellingto the antenna structure 16 at an angle to the centerline 28, theantenna provides less gain. For the dish-type antenna 16 shown in FIG.2, the antenna gain decreases as the angle to the centerline 28increases up to a certain angle on either side of the centerline. Atangles outside of this certain angle, the gain may remain fairlyconstant. It will be understood that the angle from the centerline 28may be in the horizontal direction, vertical direction, or both.

As the antenna gain decreases with the increased angle from thecenterline 28, an angle is reached at which the antenna gain isinsufficient to develop a usable satellite input signal from the antenna16 for a particular satellite transmission. The maximum reception angleat which the antenna 16 will develop a usable signal is shown as d maxin FIG. 1. The cone-shaped area defined by the angle d max about thecenterline 28 is commonly referred to as the “look angle” or aperture ofthe antenna. Satellite signals at the designated power level propagatingto the antenna 16 at an angle greater than d max to the antennacenterline 28 result in input signals from the antenna less than theminimum usable input signal level. Signals below the minimum usableinput signal level cannot be distinguished from background or noiseproduced by the antenna, and the signal processing equipment whichreceives the input signals cannot extract data from signals at these lowsignal levels. The minimum usable input signal level is determined bymany factors including the bandwidth of the transmissions, the antennastructure, and the signal processing equipment which receives thesignals developed by the antenna structure.

Referring to FIGS. 1 and 2, the satellite receiving antenna 16 which maybe at location 14 is in a satellite reception position and is directedto receive signals from one of the satellites, satellite 12 d forexample. The azimuth and elevation at which the first antenna 16 must bedirected for optimally receiving signals from satellite 12 d may be, forexample, 247.3 degrees and 25.7 degrees, respectively.

In the orientation shown in FIG. 1, the satellite receiving antenna 16at location 14 cannot receive signals from the terrestrial transmitter20 in the presence of satellite signals at the same frequency. Twofactors combine to prevent interference between the satellite andterrestrial signals. First, signals transmitted from the terrestrialtransmitter 20 travel along a wireless transmission route 40 to thelocation 14 which lies outside of the look angle of the satellitereceiving antenna 16. Thus, the terrestrial signals receive relativelylow gain from the satellite receiving antenna 16 as compared to thesatellite signals travelling along a satellite signal route 42 withinthe look angle of the antenna. Second, the terrestrial transmissionpower level is controlled according to the invention such thatterrestrial signals at the location 14, with the low gain provided bythe antenna 16 for signals travelling along wireless transmission route40, result in terrestrial input signals from the antenna 16 which arebelow the interference level with respect to the satellite input signalsfrom the antenna. Thus, even though the terrestrial signals may actuallybe picked up by the antenna 16 and produce terrestrial input signalsfrom the antenna, the satellite input signals are in comparison strongenough for the signal processing equipment associated with the antennato discriminate between the satellite and terrestrial input signals. Theinterference level will depend on several factors including primarilythe signal processing equipment and, with present technology, may be inthe range of 3 dB to 5 dB below the level of the satellite inputsignals.

Although the direction of the terrestrial transmissions along wirelessroute 40 and terrestrial signal power level combine to prevent theterrestrial signals from interfering with the satellite signals at thesame frequency, the power level of the terrestrial transmissions isstill sufficient to produce a usable signal at the location 14. In orderto receive terrestrial signals at the location, a terrestrial receivingantenna such as the antenna 18 shown in FIG. 2 is required. Theterrestrial receiving antenna 18 has a directional gain characteristicsimilar to the satellite receiving antenna 16 to ensure that theterrestrial signals produce an input which may be discriminated from theinput produced by the satellite signals at the terrestrial antenna. Forexample, the terrestrial receiving antenna 18 at location 14 could haveits centerline 30 aligned directly with the wireless transmission route40 from the terrestrial transmitter 20. The directional reception rangeor look angle from the centerline of the antenna 18 is shown as r max inFIG. 1. At this orientation, the satellite signals are well outside thelook angle of the terrestrial receiving antenna 18 and receive muchlower gain as compared to the terrestrial signals. The terrestrialsignals at that location 14 are strong enough that, with the help of thegain provided by the terrestrial receiving antenna 18, they result interrestrial input signals that may be discriminated from any inputsignals at the terrestrial receiving antenna resulting from thesatellite signals. With present technology the terrestrial input signalsfrom the terrestrial receiving antenna 18 may be 3 dB to 5 dB or moreabove the power level of the satellite input signals from theterrestrial receiving antenna in order for the terrestrial input signalsto be discriminated. Thus, the terrestrial transmission apparatus andmethod according to the invention allows satellite and terrestrialsignals carrying entirely different information or data to be receivedand used simultaneously at user location 14.

The ability to transmit terrestrial signals at the same frequency assatellite signals without interference between the signals presents anopportunity for terrestrial reuse of spectrum previously reservedexclusively for satellite transmissions. Furthermore, since theterrestrial transmitter according to the invention has a limitedeffective transmission range, the spectrum reused for the terrestrialtransmissions may also be reused for terrestrial transmissions in manydifferent geographic areas.

It will be understood that the terrestrial receiving antenna 18 at thelocation 14 or any other user location, is not an element of the presentinvention. The terrestrial receiving antenna 18 is disclosed anddiscussed herein only for the purpose of emphasizing the utility of theterrestrial transmitting apparatus and method according to theinvention. The satellite receiving antenna 16 is also not an element ofthe invention. Rather, the satellite receiving antenna 16 is discussedherein for the purpose of describing the manner and direction in whichterrestrial signals must be transmitted according to the invention. Inany case, the satellite and terrestrial receiving antennae which may beat any user location 14 need not be combined into a single structure.The combined structure 22 shown in FIG. 2 is shown for convenience indescribing the terrestrial transmission invention disclosed herein.

In the case of an omni-directional satellite receiving antenna, theantenna has no centerline such as centerline 28 shown in FIGS. 1 and 2,and no look angle or directional reception range. Rather, the gainprovided by the antenna is substantially independent of the directionfrom which the signals reach the antenna. In that case, the method ofthe invention includes transmitting terrestrial signals at the firstfrequency similarly to the case described above in which the satellitereceiving antenna is a directional antenna. However, the direction atwhich the terrestrial signals are transmitted cannot be relied upon toproduce terrestrial input signals below the interference level withrespect to the satellite input signals received at the omni-directionalsatellite receiving antenna . Rather, for the omni-directional satellitereceiving antenna, the terrestrial transmission power level iscontrolled so that the terrestrial signals present at the user locationare below the interference level with respect to the satellite signalsat the user location. Since the omni-directional antenna provides thesame gain to both the terrestrial and satellite signals, this signallevel present at the satellite receiving antenna location ensures thatthe terrestrial input signals are below the interference level withrespect to the satellite input signals.

Referring to FIG. 3, a plurality of terrestrial transmitters 32 may berequired to provide terrestrial signals strong enough to be receivedover a large area, but low enough to prevent interference with satellitesignals at the same frequency. Each transmitter 32 in FIG. 3 transmitsdirectionally in an azimuth range A of approximately 180 degrees and outto an effective reception range R. Thus, each transmitter 32 transmitsto an effective transmission area 43. With this transmitter spacing andtransmission range, the signals from the terrestrial transmitters 32 maybe received from any location within the geographic service areacomprising the combined effective transmission areas of the severalterrestrial transmitters. Although the directional range of 180 degreesis shown for purposes of example, the terrestrial transmissions may bein other ranges within the scope of this invention. In each case,however, the terrestrial transmissions from each transmitter 32 are indirections that are outside of the satellite receiving antenna lookangle at any location and, with the terrestrial signal power limitationaccording to the invention, the terrestrial signals do not interferewith the satellite signals transmitted at the same frequency.

In another aspect of the invention, the user location itself may includea transmitter for directionally transmitting at a satellite frequency.Such transmission capability from the user location would allow wirelesscommunication both to and from the user location. The transmissions fromthe user location would be limited so as to include no direction withinthe look angle of a nearby satellite receiving antenna and would belimited as to transmission power as discussed above with regard to otherterrestrial transmissions.

In the multiple terrestrial transmitter application of the inventionsuch as the arrangement depicted in FIG. 3, it may be desirable,although not necessary, for the signals from the several transmitters 32to be synchronized. The synchronization in this sense means that eachtransmitter transmits the same data at the same frequency so that it maybe received substantially simultaneously at a user location which lieswithin the effective transmission area (the area defined by radius R) oftwo or more different transmitters. Thus, regardless of whichtransmitter 32 a user may direct their terrestrial receiving antenna to,the user receives the very same data as any other user of terrestrialsignals at that frequency in the geographic service area. Thetransmitters may have associated with them signal synchronization means44 for enabling this synchronized transmission. Those skilled in the artwill appreciate that several different arrangements may be used toprovide such synchronization. For example, the signal synchronizationmeans 44 may comprise high speed communications links such as opticalfiber or high speed electrical communications links for communicatingdata to be transmitted or synchronization signals between transmitters32. Alternatively the synchronization means 44 may comprise high gainantennae for relaying the received signals from one transmitter 32 tothe next. Any such relaying antennae and high speed communication linksare to be considered equivalent signal synchronization means accordingto the invention.

As discussed above, and referring again to FIG. 1, the power level atwhich the terrestrial signals may be transmitted must be limited toprevent interference with the satellite signals transmitted at the samefrequency. However, the transmission power must still be strong enoughto produce a usable signal level at a distant location, location 14 forexample. The power level of the terrestrially transmitted signals ishighest near the transmitter and decreases as the distance from thetransmitter increases. Thus, the transmission power is limited by themaximum terrestrial signal level at the potential satellite signal userlocation which is nearest to the terrestrial transmitter 20. The maximumterrestrial signal level at the nearest satellite user location to theterrestrial transmitter is a signal which produces a terrestrial inputsignal at a satellite receiving antenna at that nearest location whichis just below the interference level with respect to the satellite inputsignals which may be received by the satellite receiving antenna at thatlocation. The transmission power to produce signals of this strength atthe nearest location to the terrestrial transmitter 20 represents themaximum allowable transmission power and determines the effectivetransmission range or area of the terrestrial transmitter. This maximumlevel and all transmission power levels below this maximum level arenon-interfering power levels and produce non-interfering terrestrialinput signals at any satellite receiving antenna in the effectivetransmission area of the terrestrial transmitter 20.

A certain area around the terrestrial transmitter may be designated anexclusion zone and the nearest location to the terrestrial transmittermay be defined as a location at the edge of the exclusion zone. In thiscase, the transmission power of the terrestrial transmitter iscontrolled so that the terrestrial signals are just below theinterference power level at this “nearest location” at the edge of theexclusion zone. The terrestrial signal level at locations within theexclusion zone is at a level which could cause interference withsatellite signals unless the satellite receiving antenna design ismodified to increase the directionality of the antenna, that is, thedifference between the gain provided to the satellite signals and thegain provided to the terrestrial signals.

It will be apparent that the maximum power level at which terrestrialsignals may be transmitted in accordance with the invention is dependentin part upon the power level of the satellite signals at the varioususer locations. As shown in FIGS. 1 and 4, one preferred form of theinvention includes a satellite signal power level monitoring arrangementor means 46 for determining the power level of the satellite signals andfor using that power level to set the power level of the terrestrialtransmitter 20. Referring now to FIG. 4, the satellite signal powerlevel monitoring means 46 may comprise a calibrated receiver or anyother suitable device by which the satellite signal strength may bedetermined. The illustrated calibrated receiver includes a satellitereceiving antenna 48, a down-converter 50, preferably a channel selector52, and a detector amplifier 54. The illustrated calibrated receiveralso includes a comparator 56 with a variable resistance device 57connected to one comparator input. The other comparator input isconnected to receive the signal from the detector amplifier 54.Comparator 56 has its output connected transmission power adjustingmeans comprising to a level control device 58 associated with theterrestrial transmitter 20.

The illustrated transmitter 20 includes an encoder 60, which receivesand encodes an input for terrestrial transmission, and also includes amodulator 62 for providing the desired modulation for transmission. Thelevel control device 58 is interposed between the modulator 62 and anup-converter 63 which converts the signals to the desired higherfrequency for transmission. The converted signals are then amplified bythe power amplifier 64 and directed to a transmitter antenna 66.

The satellite power level monitoring arrangement 46 operates bycontinuously monitoring a satellite signal which, due to the particularsatellite orientation and/or transmission power, is most susceptible tointerference from the terrestrial transmitted signals. The satellitereceiving antenna 48 is directed to receive the signal from that mostsusceptible satellite, and the received signal is down converted to anintermediate frequency by the down converter 50.

The down converted signal may be processed by the channel selector 52 toseparate a single channel and this separated signal is then filtered andconverted to a dc voltage signal by the detector amplifier 54. This dcvoltage signal is representative of the power level of the receivedsatellite signal, and is compared to a reference signal by thecomparator 56. The reference signal is set by the variable resistance 57initially so that the comparator output is zero. At this initialsetting, the transmission power level of transmitter 20 is set at amaximum non-interfering power level. At this power level the terrestrialsignals at the various locations beyond any exclusion zone around thetransmitter 20 result in terrestrial input signals which are below theinterfering power level with respect to any satellite input signals atthe same frequency. However, as the signal power of the satellitesignals received at the antenna 48 changes over time, the output ofcomparator 56 causes the level control 58 to change the transmissionpower of the terrestrial transmitter 20 accordingly. When the satellitesignal becomes weaker than at initial conditions, the comparator 56output is less than zero and this causes the level control 58 to reducethe transmission power from transmitter 20. When the satellite signalbecomes stronger, the comparator 56 output returns toward zero and thiscauses the level control 58 to increase the transmission power totransmitter antenna 66.

The method of the invention may now be described with particularreference to FIGS. 1 and 2. A first frequency is already in use fortransmitting satellite signals from a satellite, satellite 12 d forexample, along the satellite signal 42 route to location 14. Satellitesignals are received at the location 14 with the satellite receivingantenna 16 shown in FIG. 2. Satellite receiving antenna 16 has adirectional reception characteristic with a maximum gain along theantenna centerline 28 and lower gain at angles from the antennacenterline. The satellite receiving antenna 16 is oriented in asatellite reception position in which the satellite signal route 42 iswithin a look angle d max on either side of, or about, the centerline 28of the antenna. In this satellite reception position, the satellitesignals produce a satellite input signal from the satellite receivingantenna 16 and this input signal is at least at the minimum usablesignal level for the particular signal processing equipment.

The method of the invention includes transmitting terrestrial signals atthe first frequency, that is, the same frequency at which the satellitesignals are transmitted. The terrestrial signals are transmitted indirections which include the wireless transmission route 40 from thetransmitter 20 to the location 14. According to the invention, thetransmitter 20 is located such that the wireless transmission route 40lies at an angle to the satellite receiving antenna centerline 28, andthis angle is sufficiently large that the terrestrial signals present atthe location 14 produce terrestrial input signals which are below theinterference level with respect to the satellite input signals producedat the antenna 16. The terrestrial signals present at the location 14are also at a power level at least at the minimum usable terrestrialsignal level. At this minimum useable terrestrial signal level theterrestrial signals may be picked up by a terrestrial antenna 18 whichmay be at the user location 14. The terrestrial antenna 18 is adirectional antenna to ensure that the satellite signals do notinterfere with the terrestrial signals.

Under current technology, the satellite signal level at any terrestrialuser location may range from −120dBm to −125 dBm under clear skyconditions and from −122 dBm to −127 dBm under more adverse weatherconditions. Depending primarily upon the directionality of the satellitereceiving antenna and the capabilities of the signal processingequipment associated with the satellite receiving antenna, terrestrialsignal power level at the user location must remain below about −95 dBm.This terrestrial signal power level assumes a satellite receivingantenna gain of approximately 34 dB for the satellite signals and a gainof about −2 dB for the terrestrial signals, and an interference level ofapproximately 4 dB below the satellite input signal power level. Also,under current technology, the terrestrial input signals must remainabout 4.5 dB (3 dB to 5 dB) below the satellite input signals in orderfor the signal processing equipment to distinguish the satellite inputsignals and extract the desired data from the satellite input signals.Those skilled in the art will readily appreciate that the invention isnot limited to these signal power values and that these values areprovided for purposes of illustration and example.

Also according to the invention, the terrestrial transmitter 20transmits only along wireless transmission paths which avoidinterference with the satellite signals at any location within aneffective transmission range of the terrestrial transmitter. That is,the wireless route 40 from the transmitter 20 to any location 14 is atan angle with respect to a properly aligned satellite receiving antennaat the respective location such that the terrestrial input signals fromthe satellite receiving antenna are always below the interference levelwith respect to the satellite input signals which may be produced fromthe satellite receiving antenna. To ensure the required terrestrialsignal strength at any location, including those adjacent to theterrestrial transmission location, the method of the invention may alsoinclude monitoring the signal strength of the satellite signals andsetting the terrestrial transmission power to the maximumnon-interfering power level based upon that detected satellite signalstrength.

Referring to FIG. 3, the method also includes transmitting from a secondterrestrial transmitter 32 to a second location which may be anylocation within range R from the second terrestrial transmitter. Thewireless route from the second transmitter to the second location is atan angle to a properly oriented satellite receiving antenna at thesecond location to produce terrestrial input signals below theinterference level with respect to the satellite input signals whichresult from satellite signals received by the satellite receivingantenna at the second location.

EXAMPLE

A test was conducted using a mobile test antenna. The test equipmentincluded a DBS receiving antenna connected to signal processingequipment. The signal processing equipment was connected to receiveinput signals from the DBS receiving antenna and operated to direct adesired channel output to a television. The DBS receiving antenna was adirectional antenna providing a gain of between 31 dB and 34 dB across alook angle of approximately 5 degrees on either side of the antennacenterline. Antenna gain from the DBS receiving antenna ranged from −2dB to −16 dB outside of the antenna look angle.

The test used a terrestrial transmitter having a directional transmitterantenna elevated to 52 feet AGL and directed with its peek power outputat an azimuth of 180 degrees (due South), with true horizontal polarity.The terrestrial transmitter set up was not changed from thisconfiguration throughout the test. Only the transmission power wasvaried as will be discussed below.

The interference test was conducted at several different test locationsor user locations, each spaced apart from the terrestrial transmitterlocation. At each test location the DBS receiving antenna was firstelevated to achieve a line of sight to the terrestrial transmitter andthen oriented with its centerline aligned generally with the wirelesstransmission route from the terrestrial transmitter. Once a line ofsight was verified between the DBS test antenna and the terrestrialtransmitter, an isotropic receive power level was established from theterrestrial transmitter at full power, 29 dBm.

At each test location the DBS receiving antenna was then optimallypositioned for receiving satellite signals from a particular DBSsatellite, that is, the centerline of the DBS receiving antenna wasaligned with the signal route from the satellite. The satellite signalsat a particular frequency were received and fed to the televisionassociated with the test apparatus. At each test site, the wirelesstransmission route from the terrestrial transmitter to the test site wasoutside of the look angle of the DBS receiving antenna optimallypositioned for receiving satellite signals from the DBS satellite. Theterrestrial transmitter was operated to transmit at the same frequencyas the received satellite signals, 12.470 gigahertz. In each test ifthere was interference with the received DBS satellite signals, asindicated by imperfect television reception, the terrestrial transmitterpower was reduced until no interference was produced and this level,that is, the power level just below the interference level, wasrecorded.

At the weather conditions at which the tests were conducted, thesatellite signal power level at each test site is calculated to beapproximately −125 dBm. Under these conditions a terrestrialtransmission power level of 13 dBm produced an exclusion zone in thetransmission directions around the terrestrial transmitter ofapproximately one quarter mile while producing useable terrestrialsignals at a location approximately 9.9 miles away from the terrestrialtransmitting antenna. It is estimated that the terrestrial signal powerlevel at this test site was approximately −137 dBm.

The above described preferred embodiments are intended to illustrate theprinciples of the invention, but not to limit the scope of theinvention. Various other embodiments and modifications to thesepreferred embodiments may be made by those skilled in the art withoutdeparting from the scope of the following claims.

What is claimed is:
 1. A method for reusing a first transmissionfrequency already in use for transmitting satellite signals from asatellite along a satellite signal route to a first location forreception at a satellite receiving antenna which may be at the firstlocation, the satellite receiving antenna producing a maximum gain forsignals received along a satellite receiving antenna centerline and lessgain at angles from said centerline, the satellite signals having asignal power level at the first location such that, when the satellitereceiving antenna is placed in a satellite reception position in whichthe satellite transmission route lies within a satellite reception lookangle about the satellite receiving antenna centerline, the satellitesignals produce satellite input signals from the satellite receivingantenna which are at least at a minimum usable satellite input signallevel, the method comprising the steps of: (a) substantiallycontinuously detecting the satellite signal power level at a locationnear a first terrestrial transmitter; (b) setting the transmission powerof the first terrestrial transmitter to a non-interfering level basedupon the satellite signal power level detected near the firstterrestrial transmitter, the non-interfering level being a levelensuring that substantially each location within an effectivetransmission area around the first terrestrial transmitter receivesterrestrial signals from the first terrestrial transmitter at a powerlevel to produce non-interfering terrestrial input signals from asatellite receiving antenna aligned to receive satellite signals at saidlocation, the non-interfering terrestrial input signals being at a powerlevel less than an interference level with respect to the satelliteinput signals produced by the satellite receiving antenna at saidlocation; and (c) transmitting terrestrial signals at the firsttransmission frequency from the first terrestrial transmitter, theterrestrial signals being transmitted in directions including a wirelesstransmission route from the first terrestrial transmitter to the firstlocation, and the wireless transmission route lying at an angle from thesatellite receiving antenna centerline, when the satellite receivingantenna is in the satellite reception position, such that theterrestrial signals present at the first location result in terrestrialinput signals from the satellite receiving antenna which are at a powerlevel less than the interference power level with respect to thesatellite input signals, the terrestrial signals present at the firstlocation having a power level at least at a minimum usable terrestrialsignal level.
 2. The method of claim 1 wherein the step of detecting thesatellite signal power level includes the steps of: (a) receiving thesignals transmitted from the satellite at the first transmissionfrequency; and (b) converting the signals transmitted from the satelliteat the first transmission frequency to a representative signal which isrepresentative of the satellite signal power level.
 3. The method ofclaim 2 wherein the step of setting the transmission power level for thefirst terrestrial transmitter includes the step of: (a) comparing therepresentative signal to a reference signal to produce a comparisonoutput.
 4. The method of claim 3 further including the step of: (a)using the comparison output to control the transmission power level forthe first terrestrial transmitter.
 5. The method of claim 4 wherein thestep of using the comparison output to control the transmission powerlevel for the first terrestrial transmitter includes the step of: (a)controlling a modulated signal level in the first terrestrialtransmitter.
 6. An apparatus for simultaneously providing terrestriallytransmitted signals on a common frequency with satellite signalstransmitted from a satellite along a satellite signal route to a firstlocation, the satellite signals being transmitted at a first frequencyfor reception at a satellite receiving antenna which may be at the firstlocation, the satellite receiving antenna producing a maximum gain forsignals received along a satellite receiving antenna centerline and lessgain at angles to said centerline, the satellite signals having a signalpower level such that, when the satellite receiving antenna is placed ina satellite reception position in which the satellite transmission routelies within a satellite reception look angle about the satellitereceiving antenna centerline, the satellite signals result in satelliteinput signals from the satellite receiving antenna which are at least ata minimum usable satellite input signal level, the apparatus comprising:(a) a first terrestrial transmitter for transmitting signals at thefirst frequency along a wireless transmission route from a firstterrestrial transmitter location to the first location, the wirelesstransmission route lying at an angle from the satellite receivingantenna centerline, when the satellite receiving antenna is in thesatellite reception position, such that the terrestrial signals presentat the first location result in terrestrial input signals from thesatellite receiving antenna which are at a power level less than aninterference level with respect to the satellite input signals, theterrestrial signals present at the first location having a power levelat least at a minimum usable terrestrial signal level; (b) satellitesignal power monitoring means for substantially continuously detectingthe satellite signal power level at a location near the firstterrestrial transmitter; and (c) transmission power adjusting meansassociated with the first terrestrial transmitter for setting thetransmission power of the first terrestrial transmitter to anon-interfering level based upon the satellite signal power leveldetected by the satellite signal power monitoring means, thenon-interfering level being a level ensuring that substantially eachlocation within an effective transmission area around the firstterrestrial transmitter receives terrestrial signals from the firstterrestrial transmitter at a power level to produce non-interferingterrestrial input signals from a satellite receiving antenna aligned toreceive satellite signals at said location, the non-interferingterrestrial input signals being at a power level less than theinterference level with respect to the satellite input signals producedby the satellite receiving antenna at said location.
 7. The apparatus ofclaim 6 wherein the satellite signal power monitoring means includes:(a) a satellite signal receiving antenna aligned to receive signalstransmitted from the satellite at the first transmission frequency; and(b) a detector amplifier operatively connected to convert the signalsreceived by the satellite signal receiving antenna to a representativesignal which is representative of the satellite signal power level. 8.The apparatus of claim 7 wherein the satellite signal power monitoringmeans further includes: (a) a comparator operatively connected tocompare the representative signal to a reference signal to produce acomparison output.
 9. The apparatus of claim 8 wherein the transmissionpower adjusting means includes a level control device operativelyconnected to the first terrestrial transmitter and wherein thecomparator is connected to apply the comparison output to the levelcontrol device.
 10. The apparatus of claim 9 wherein the level controldevice is operatively connected to an output of a modulator associatedwith the first terrestrial transmitter, the level control device forcontrolling a modulated signal level in the first terrestrialtransmitter.
 11. An apparatus for simultaneously providing terrestriallytransmitted signals on a common frequency with satellite signalstransmitted from a satellite, the satellite signals being transmitted ata first frequency along a satellite transmission route to a satellitereceiving antenna at a location which may be anywhere within ageographic service area, the satellite receiving antenna producing amaximum gain for signals received along a satellite receiving antennacenterline and less gain at angles from said centerline, the satellitesignals having a signal power level which, when the satellite receivingantenna is placed at a satellite reception position in which thesatellite transmission route lies within a satellite reception lookangle about the satellite receiving antenna centerline, results insatellite input signals from the satellite receiving antenna, thesatellite input signals being at least at a minimum usable satelliteinput signal level, the apparatus comprising: (a) a plurality of spacedapart terrestrial transmitters, each terrestrial transmittertransmitting terrestrial signals at the first frequency, the pluralityof spaced apart terrestrial transmitters being arranged such thatsubstantially each respective location within the geographic servicearea has a wireless transmission route to one of the terrestrialtransmitters, the wireless transmission route lying at an angle from thesatellite receiving antenna centerline when the satellite receivingantenna is in the satellite reception position at the respectivelocation such that the terrestrial signals present at the respectivelocation are at least at a minimum usable terrestrial signal level butresult in terrestrial input signals from the satellite receiving antennawhich are at a power level less than an interference level with respectto the satellite input signals; (b) satellite signal power monitoringmeans for substantially continuously detecting the satellite signalpower level at a monitoring location within the geographic service area;and (c) transmission power adjusting means associated with theterrestrial transmitters for setting the transmission power of theterrestrial transmitters to a non-interfering level based upon thesatellite signal power level detected by the satellite signal powermonitoring means, the non-interfering level being a level ensuring thatsubstantially each location within the geographic service area receivesterrestrial signals from each of the terrestrial transmitters at a powerlevel to result in non-interfering terrestrial input signals from asatellite receiving antenna aligned to receive satellite signals at saidlocation, the noninterfering terrestrial input signals being at a powerlevel less than the interference level with respect to the satelliteinput signals produced by the satellite receiving antenna at saidlocation.
 12. The apparatus of claim 11 wherein the satellite signalpower monitoring means includes: (a) a satellite signal receivingantenna aligned to receive signals transmitted from the satellite at thefirst transmission frequency; and (b) a detector amplifier operativelyconnected to convert the signals received by the satellite signalreceiving antenna to a representative signal which is representative ofthe satellite signal power level.
 13. The apparatus of claim 12 whereinthe satellite signal power monitoring means further includes: (a) acomparator operatively connected to compare the representative signal toa reference signal to produce a comparison output.
 14. The apparatus ofclaim 13 wherein the transmission power adjusting means includes a levelcontrol device operatively connected to the first terrestrialtransmitter and wherein the comparator is connected to apply thecomparison output to the level control device.
 15. The apparatus ofclaim 14 wherein the level control device is operatively connected to anoutput of a modulator associated with the first terrestrial transmitter,the level control device for controlling a modulated signal level in thefirst terrestrial transmitter.
 16. A method for reusing a firsttransmission frequency already in use for transmitting satellite signalsfrom a satellite along a satellite signal route to a first location forreception at a satellite receiving antenna which may be at the firstlocation, the satellite receiving antenna producing a maximum gain forsignals received along a satellite receiving antenna centerline and lessgain at angles from said centerline, the satellite signals having asignal power level at the first location such that, when the satellitereceiving antenna is placed in a satellite reception position in whichthe satellite transmission route lies within a satellite reception lookangle about the satellite receiving antenna centerline, the satellitesignals produce satellite input signals from the satellite receivingantenna which are at least at a minimum usable satellite input signallevel, the method comprising the steps of: (a) determining the satellitesignal power level; (b) setting the transmission power of a firstterrestrial transmitter to a non-interfering level based upon thedetermined satellite signal power level, the non-interfering level beinga level ensuring that substantially each location within an effectivetransmission area around the first terrestrial transmitter receivesterrestrial signals from the first terrestrial transmitter at a powerlevel to produce non-interfering terrestrial input signals from asatellite receiving antenna aligned to receive the satellite signals atsaid location, the non-interfering terrestrial input signals being at apower level less than an interference level with respect to thesatellite input signals produced by the satellite receiving antenna atsaid location; and (c) transmitting terrestrial signals at thenon-interfering power level and first transmission frequency from thefirst terrestrial transmitter to the effective transmission area. 17.The method of claim 16 wherein the step of determining the satellitesignal power level includes the steps of: (a) receiving the signaltransmitted from the satellite at the first transmission frequency; and(b) converting the signal transmitted from the satellite at the firsttransmission frequency to a representative signal which isrepresentative of the satellite signal power level.
 18. The method ofclaim 17 wherein the step of setting the transmission power level forthe first terrestrial transmitter includes the step of: (a) comparingthe representative signal to a reference signal to produce a comparisonoutput.
 19. The method of claim 18 further including the step of: (a)using the comparison output to control the transmission power level forthe first terrestrial transmitter.
 20. The method of claim 19 whereinthe step of using the comparison output to control the transmissionpower level for the first terrestrial transmitter includes the step of:(a) controlling a modulated signal level in the first terrestrialtransmitter.